docs: remove the section titles that have no items

Author: kenjis

user_guide_src/source/installation/upgrade_434.rst

@@ -12,9 +12,6 @@ Please refer to the upgrade instructions corresponding to your installation meth
     :local:
     :depth: 2
 
-Mandatory File Changes
-**********************
-
 Breaking Changes
 ****************
 
@@ -37,9 +34,6 @@ specify the ``null`` key.
 Note that the bug may have changed unexpected NULL constraints in previous
 versions.
 
-Breaking Enhancements
-*********************
-
 Project Files
 *************